How is this relative strength index RSI @Binance BiBi calculated? In general, what range does this index indicate is the best buying period at the bottom of a bear market?

The relative strength index (RSI) of Bitcoin has fallen to 17, marking its third lowest level of oversold in history. According to NS3, only the RSI was lower during the bottom of the 2018 bear market and the Covid crash in 2020.

This extreme oversold condition often signals that the price may experience significant upward fluctuations.